Nearly 40,000 public schools were surveyed in the study. The average start time was 8:03 a.m., but there were big differences among states:

All schools in Hawaii, Mississippi and Wyoming started before 8:30 a.m.

Most schools in Alaska and North Dakota started at 8:30 a.m. or later.

Louisiana had the earliest average school start time - 7:40 a.m.

Alaska had the latest start-time average - 8:33 a.m.

The reason it matters, doctors say, is that adolescents should sleep, at a minimum, between 8.5 and 9.5 hours a night.

Lack of sleep “is common among high school students and is associated with several health risks such as being overweight, drinking alcohol, smoking tobacco, and using drugs – as well as poor academic performance,” according to the CDC, citing a 2013 study.